1. Field of the Invention
This invention relates to cameras having an external light measuring device and, more particularly, to cameras in which a correction is factored into the exposure value obtained from the light measuring device when exposure is controlled.
2. Description of the Related Art
In recent years, as the camera using a silver-halide film and adapted to beginners, a small-sized, easy-to-handle, compact type is widespread. Yet, even in these compact type cameras, there are an increasing number of cameras of such a model that close-up photography is made possible by increasing a quantity of the total focusing movement.
Even with the electronic camera using a CCD or like photoelectric transducer element as the photographic material, a similar trend to that of the aforesaid camera using a silver-halide film is occurring so that a camera of the small-sized, easy-to-handle, compact type adapted to general users and capable of close-up photography is about to be announced.
And, even these cameras of the compact type are desired to have zooming, automatic exposure, and automatic focusing functions. This tends to put the increase of the complexity of structure of the operating mechanism and the demand for the compact form in conflict with each other.
While the silver-halide film has relatively wide latitude in its development, the exposure latitude of the CCD or like photoelectric transducer is very narrow. In the electronic camera using such a photoelectric transducer, therefore, when shooting, the exposure must be controlled with high accuracy.
Furthermore, to round up the photographic lens in compact form, part of the zooming provision may be made in the lens component behind the diaphragm. With the use of this, when zooming, the virtual effective value of the aperture size, or F-number, changes although the real size of the aperture opening remains unchanged. Hence, it has been the practice to incorporate into the camera a capability of controlling the exposure correction in accordance with the zooming position by increasing or decreasing the size of opening of the diaphragm aperture. But, as for the change of F-number resulting from focusing, from the reason that it is relatively little, and in view of the difficulty of advancing the compact unit production technique, the exposure correcting function for focusing has not been incorporated into the camera.
In the case of focusing by moving the lens component behind the diaphragm, however, because the range of variation with focusing of the F-number is relatively large, particularly for the electronic camera of narrow latitude, or for the camera with which one seeks rich gradation of tone and much more beauty in the picture, there arises a problem, in that the exposure error is so large as not to be acceptable.